The present invention relates to an oxygen absorbent according to the preamble of claim 1 and to the use thereof.
Such an oxygen absorbent is e.g. known from DE-2836876 C2.
Oxygen absorbents are used to keep fresh or preserve packaged foods, such as e.g. dried milk, ground coffee, rough-ground grain, certain sausage and meat products, chocolates, fat-containing long-life pastries, etc. In this way it is also possible to prevent oxidative decomposition of sensitive medicaments.
Keep-fresh bags with oxygen-absorbing iron products according to the above teaching have long been known and used. During the packaging of the food or medicaments, said bag is added to the pack. The packs are then immediately sealed in a gas-tight foil or film, so that immediately following packing the oxygen content of the pack is irreversibly absorbed by the oxygen-absorbing substance.
However, iron-containing products suffer from the disadvantage that in the case of an accidental destruction of the bag the iron product together with its catalyst is mixed with the food and is possibly eaten. Intentional or unintentional consumption can also not be excluded. From the consumer safety standpoint, such products should consequently not be used.
The same applies with respect to the also known keep-fresh bags based on ascorbic acid. For the activation of the oxygen absorption of the ascorbic acid, it is necessary to add heavy metal salts, so that there are also in this case serious reservations regarding consumer safety.
The problem of the present invention is therefore to improve the aforementioned agents in such a way that the aforementioned disadvantages are avoided. It must be suitable for use in a bag as a food preserving agent and must be safely mixable or edible with the food. Other use forms consist of the addition in tablet form to a pack, or fixing to a pack. It must also be possible to incorporate in a composite foil or film made from one-sided gas-permeable and gas-impermeable material. In this use form the gas-permeable film faces the product to be protected, so that the oxygen to be absorbed passes through the permeable film to the absorbing agent. This use form has the advantage that the consumer does not perceive, at least not in a disturbing manner, the oxgyen absorber. The same applies regarding the use of the pack in connection with medicaments.
A possible system for this purpose is the combination of glucose and glucose oxidase.
A further requirement from the practical use of the keep-fresh bag is that the oxygen is absorbed within a pack in a short time, i.e. between hours and max 1 to 2 days, otherwise the decay of the food induced by the oxygen can commence.
There were considerable, hitherto unsolved difficulties in connection with the use of glucose and glucose oxidase. According to the prior art the more liquid (water) that is available for the diffusion of the reactants with respect to one another and for the conveying away of the reacted products the better functions the enzymes and the substance combinations. Thus, enzymatic reactions take place most quickly in a liquid product, the reaction speed attainable being a decisive factor for economics and usability. However, according to the existing teaching the less water is present, the slower an enzymatic reaction takes place.
The liquid to pasty combinations of glucose and enzymes prepared according to this prior art had completely inadequate oxygen absorption from the time standpoint and even after several days could not completely absorb the oxygen from the packs.
Naturally it is possible to increase the reaction or absorption rate by increasing glucose oxidase addition. However, glucose oxidase is a very expensive product and this procedure would not be economically appropriate. In fact, the necessary economics are only attainable through minimizing the glucose oxidase proportion.
Silicic acids for combination with liquids have been used in practice for many years. They have a very large surface per weight unit and are in part present as almost spherical particles. A silicic acid with an average particle diameter of 100 my e.g. has a surface of approximately 200 m.sup.2 /g.
The first tests with silicic acid were carried out in accordance with the prior art. Comparatively large water quantities and corresponding glucose and glucose oxidase quantities were mixed with the silicic acid to a pasty mass and once again led to completely inadequate oxygen absorption rates.